A voltage reference is typically provided by electronic circuitry that provides at an output of the circuitry a constant voltage that does not fluctuate even when there are variations in temperature or the power supply that might normally or otherwise cause fluctuations in the voltage. As a result, the hope is that the voltage reference can provide a point of reference even as conditions in the system can vary. Voltage references can be used in power supply voltage regulators, analog-to-digital converters, digital-to-analog converters as well as many other measurement and control systems. Generally, a voltage reference can be created by balancing a voltage that increases with temperature increases with a voltage that decreases with temperature increases.
A voltage that is proportional to absolute temperature (PTAT) increases with temperature increases and is known as a PTAT voltage. A voltage that is complementary to absolute temperature (CTAT) can decrease with temperature decreases and is known as a CTAT voltage. A voltage reference can be based on a bandgap principle where a transistor base-emitter voltage, which is intrinsically complementary to absolute temperature, CTAT, is added to a voltage which is proportional to absolute temperature, PTAT. If the two voltage components are well balanced the compound voltage is at a first order compensated against temperature variations. The problem with traditional voltage references is related to instability of the reference over time. This instability is known as drift and is mainly attributed to the CTAT voltage component. This has an absolute magnitude and is dependent on many process parameters.
There is therefore a continued desire for a stable voltage reference that has reduced drift characteristics.